Industrial coffee dispensers, such as the ones commonly found in offices or shopping malls, all comprise a coffee maker controlled by a control unit. The control unit operate the dispenser to brew and deliver one or more types of coffee. In some dispensers the coffee maker is a reverse french press. A reverse french press includes a cylinder that acts as a mixing or brewing chamber and a piston. The piston travels up and down the extraction chamber to brew the coffee and deliver it to the customer. Examples of reverse french presses are disclosed in U.S. Pat. Nos. 5,351,604 and 5,479,849.
The piston includes a piston head and a piston rod pivotally mounted to the piston head. The piston head has a piston body covered by a piston cover, which ensures that the piston body is waterproofly connected to the extraction chamber. The piston is usually made of rigid polycarbonate and the piston cover of a slightly flexible polytetrafluoroethlene (PTFE). To secure the piston cover onto the piston body, a plate is disposed onto a top surface of the piston cover. A plurality of screws is inserted into apertures of the piston body and the piston cover to secure the plate to the piston body. Once assembled, the screw heads are facing an inside of the mixing chamber. As a result, the screw heads are in contact with the coffee during the brewing cycles. Over time coffee can accumulate in and around the screw heads. The coffee being difficult to clean in those areas, the piston head can become unhygienic.
Therefore, there is a need for an improved piston of a french press coffee maker.